Penicillins (Oral)
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Patient Guide

 Penicillins (Oral)

 Penicillins (Oral)

About your medicine

Your doctor has prescribed one of the following penicillin for you:

  • Amoxycillin
  • Amoxycillin with clavulanic acid
  • Cloxacillin
  • Penicillin

What is this medicine used for?

Penicillins are antibiotics that are used to treat and prevent a wide variety of bacterial infections. It works by stopping the growth of bacteria.

How should you take this medicine?

The dosage is based on your medical condition and response to therapy. Antibiotics work best when the amount of medicine in your body is kept at a constant level. Therefore, take this drug at evenly spaced intervals.

Continue to take this medication until the full-prescribed amount is finished, even if symptoms disappear after a few days. Stopping the medication too early may allow bacteria to continue to grow, which may result in a relapse of the infection.

Penicillin and Cloxacillin are best absorbed when taken on an empty stomach (half to one hour before food).

Amoxycillin and Amoxycillin and clavulanic acid should be taken with or after food.

What should you do if you forget a dose?

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule.

Do not double the next dose to make up for the missed dose.

What possible side effects may it cause?

Certain side effects of this medicine are not unusual and may even disappear during treatment. If any of the following effects persist or are severe, consult your doctor.

  • diarrhoea
  • nausea, vomiting
  • stomach upset or discomfort

Although uncommon, you may develop a black, "hairy" tongue while taking penicillin. This effect is harmless and usually goes away after treatment. Maintain good oral hygiene, and brush your tongue with a soft toothbrush twice a day.

Consult your doctor as soon as possible if any of these additional effects occur, as they may indicate more serious side effects:

  • allergic reaction (difficulty breathing, severe dizziness, rash, itching, swelling)
  • sores in the mouth, red painful eyes or blisters on the skin
  • vaginal itching or discharge
  • white spots on lips or in mouth

This medication may rarely cause a severe intestinal condition (pseudomembranous colitis) due to a resistant bacteria. This condition may occur during treatment or weeks after treatment has stopped. Do not use anti-diarrhea products or narcotic pain medications if you have the following symptoms because these products may make them worse. Tell your doctor immediately if you develop: persistent diarrhoea, abdominal or stomach pain/cramping, blood/mucus in your stool.

What precautions should you take?

  • Inform your doctor if you have kidney problems, if you are allergic to penicillins or to cephalosporins (e.g., cephalexin, cefuroxime) or if you have any other allergies
  • For women: Tell you doctor if you are pregnant, plan to become pregnant, or are breast-feeding. This medication should be used only when clearly needed during pregnancy.
  • Inform your doctor if you are taking any other medications such as methotrexate, antibiotics (e.g. tetracyclines), blood thinners (e.g. warfarin), probenecid, and oral contraceptive.
  • Inform your doctor if you are also taking any vitamins or herbal supplements.
  • This medication may decrease the effectiveness of combination-type birth control pills. This can result in pregnancy. You may need to use an additional form of reliable birth control while using this medication.
  • Do not allow anyone else to take this medication.

How do you store this medicine?

  • Follow the instructions on the label about the expiry date, and on the need for refrigeration of the oral liquid form of the medicine. Do not freeze. Discard any unused portion after the duration as stated on the label.
  • Keep this medicine away from heat and direct sunlight in a cool, dry place, out of reach of children.
  • Do not keep this medicine with other medications in the same container. Keep each medicine separately in labeled containers.

When in doubt, consult your doctor or pharmacist.
National Skin Centre (Singapore)
1 Mandalay Road, Singapore 308205
Tel: 63508454


Last updated on 05 May 2020

Last updated on 05 May 2020